build secure-config on stable-2.13 branch

Change-Id: Ic79172de7b93c96bf497e2219ccfae3ee6075c64
diff --git a/jenkins/gerrit-buck-plugin-secure-config.yaml b/jenkins/gerrit-buck-plugin-secure-config.yaml
index 7ebc3c7..e255b07 100644
--- a/jenkins/gerrit-buck-plugin-secure-config.yaml
+++ b/jenkins/gerrit-buck-plugin-secure-config.yaml
@@ -2,6 +2,7 @@
     name: secure-config
     branch:
       - master
+      - stable-2.13
     jobs:
       - 'plugin-{name}-{branch}'